Production of sheet materials



Patented June 1,1943

Philip Richard Hawtin and Cyril Gardner, Spondon, near Derby, England, assignors to Celanese Corporation of America, a corporation of Delaware No Drawing. Application January 25, 1941, Serial No. 375,952. In Great Britain January 16,

6 Claims.

This invention relates to the production of sheet materials and in particular sheet materials having a basis of cellulose acetate or' like filmforming substance. The principal object of the invention is to provide a simple method for the production of such sheet materials of any desired thickness, which does not involve the use of expensive plant such as the straightening and polishing presses which are necessary when the sheet materials are cut from a block of the film-forming substance.

We have found that the object referred to above can be realised by casting a' solution of the filmforming substance in a volatile solvent onto the surface of a flat layer of soap or a soap-like substance suitably supported, removing volatile solvent by evaporation, repeating these operations if necessary to obtain a sheet of the desired thickness, stripping the sheet from the support and removing any adhering soap or the like by means of a liquid which is a solvent for the soap but not for f the film-forming substance. The sheet, even when ofconsiderable thickness, e. g. 0.01 to 0.1 inch or even thicker, can readily be removed from the supporting layer whereas when sheets are cast directly onto the surface of glass or like hard material, difflculty is experienced in removing the sheet unless it be sufliciently flexible to be rolled back on itself. preciated therefore, that the process of the invention ofiers special advantages in connection metal. Glass is generally to be preferred as flat,

highly polished platesof glass can more easily and more cheaply be obtained than plates of metal having the desired flatness and polish. The soap may be applied to the plate in solutionin a suitable solvent; e. g. 'alcohol, by spray- It will be 'ap-' drawn. The sheet material may then be cast directly onto the upper surface of the block of soap.

To avoid premature stripping owing to contraction of the sheet material as the solvent evapcrates, it is of advantage to provide around the surface of soap or the like a surface, e. g.,of untreated glass or' metal, to which the sheet material readily adheres and to cast the sheet so that it-extends beyond the soap or the like and so has its edges anchored to the untreated glass or metal. With the same object in view, when a solid block of soap or the like is formed in. a tray to provide the casting surface, the tray may with advantage be provided with a flat horizontal flange round its edges to form a surface flushwith that of the soap for the edges of the sheet to adhere to.

ing or other suitable method, e. g. brushing, and

' dried and polished to form a coherentlayer of uniform thickness. The layer of soap may be extremely thin, e. g. considerably less than 0.001

inch in thickness. Alternatively, ,a thick layer or 1 block of soap or the like may be formed by any suitable method, for instance by melting the soap and running it into a tray, e. g. of iron, which need not have a perfectly flat bottom. If necessary, to ensure the flatness of the upper surface of the block of soap or the like, the said surface may be formed by pressing on to the block of soap the flat polished surface of. a block of glass, metal or other suitable former which is then with- 'ethyl and dibutyl tartrates.

It is preferable to build thick -films up from several layers. This isnot essential but when a thick sheet is cast in a single stage removal of the volatile solvent is a, slower operation. The

. sheets may, ,before and after stripping, be seasoned in a warm atmosphere to reduce still 'may be made of triacetin, 'dimethyl phthalate,

dimethoxy ,ethyl phthalate, dibutyl' phthalate, diethoxy-ethyl phthalate, methyl methoxy ethyl phthalate, ethyl ethoxy-ethyl phthalate, and di- Plasticisers which are without substantial afllnity for the cellulose acetate but which are useful with a'view to increasing the flre resistance of the sheet material, e. g. tricresyl phosphate, triphenyl phosphate and trichloro-ethyl phosphate may be present in the composition, preferably in admixture with plasticisers having a high affinity for cellulose acetate, e. g. triacetin.- 'I'he composition may also contain volatile solvents for cellulose acetate other than acetone, e. g. dioxane or methylene ethylene ether, high boiling solvents e. g. diacetone alcohol and ethyl lactate, and colouring agents or used on a'flat' plate or glass or other suitable support, the soap may be soft. Strongly alkaline soaps should not be used in casting sheet materials of saponiflable esters ich as cellulose\ acetate on account of the danger of saponiflcation. Excellent results have been obtained using sodium stearate and sodium palmitate as the soaps. Other alkali metal salts of long-chain fatty acids may be used as may the corresponding salts of nitrogenous bases, e. g. ammonia and the alkylolamines. Useful examples of such soaps of nitrogenous bases are the stearate palmitate and oleate of triethanolamine. Other substances having detergent properties,-in particularwater soluble substances containing an aliphatic hydrophobe group of at least 12 carbon atoms, e. g.

having a hydrocarbon chain of 12-18 atoms, can be used. Examples are: the sodium and potassium salts of cetyl naphthalene sulphonic acid, of sulphonated higher alcohols such as octyl, cetyl, lauryi and .oleyl alcohols, of sulphonated esters of higher alcohols such as the dihexyl and dioctyl esters of succinic acid, and of sulphated higher fatty alcohols, fatty acid amides and fatty acid esters. Salts such as those specified above but containing in place of alkali metals basic nitrogenous groups such as ammonium and univalent alkylamine and alkylolamine radicles, can

also be used. Use may also be made of the solid or substantially solid partial esters of etheralcohols containing at least two hydroxy groups with soap forming acids, e. g. the mono stearates and palmitates of diethylene glycol and triethylene glycol. I

The following examples illustrate the invention:

' Example 1 A glass plate having a flat, highly polished surface is coated on this surface with a 50% solution (by weight) of triethenolamine oleate in ethanol. By drying of! the solvent and polishing, a very thin coating of the oleate on the glass .is obtained. A margin of uncoated glass is left round the coating and the edges of the plate are provided with detachable metal sides.

The sheet is stripped from the block by removal of the side pieces. The sheet is then trimmed by I cutting oi! the marginal portions adherent to-the may be avoided by washing with aqueous solu- The coated glass plate is supported with its I coated surface horizontal and a layer of dope consisting of a 20-30% solution of cellulose acetate in acetone, the solution containing 20-30% on the weight of the cellulose acetate of dimethyl phthalate, is flowed onto the glass plate so as Y Example 2 Molten glycol stearate (the mono stearate of.

diethylene glycol) is poured into a metal tray having detachable sides. Each side has a lower vertical portion, an intermediate outwardly extending horizontal portion, and an upper vertical portion. Suflicient molten lycol stearate is poured into the tray to form when cold a block, the upper surface of which is flush with the horizontal portions of the sides.

' A sheet is built up on the block of glycol stearate by the method described in Example 1, the area of the sheet being bounded by the upper tions of the soap or the like, if necessary in progressively decreasing concentrations, and finally with water. i 1

Instead of cellulose acetate other organic flimforming substances which can be dissolved in suitable volatile liquids can be employed e. g. cellulose propionate, cellulose butyrate cellulose acetate-prop'ionate, cellulose acetate-butyrate cellulose acetate-nitrate, ethyl cellulose, benzyl cellulose, ethyl cellulose acetate and other esters, including mixed esters, ethers and ester-ethers of cellulose. The film-forming substance need not be a cellulose derivative. ILma'y, for example, be a polymerised unsaturated substance such as polyvinyl alcohol, polyvinyl acetate. polyvinyl chloride, polyvinyl chloracetate, a co-polymer of two or more of such unsaturated substances, a I

polymerised unsaturated compound derived from acrylic acid, e. g. polymethyl methacrylate, a polymerised unsaturated hydrocarbon, e. g. a polystyrene synthetic resin or any other organic film forming substance from which films, foils or the like can be made by the evaporative method. The invention is of particular importance in the production of transparent sheet materials.

The invention has been described with particular reference to the production of relatively thick sheet materials by a casting operation. The invention, however, includes quite generally the formation of sheet materials of any thickness on a surface of soap or the like by an evaporative method. Thus instead of being poured onto the soap layer' the film-forming composition may be applied by brushing or spraying. The soap layer may be supported on a metal plate or on an endless band such as is used in the continuous production of films or foils so facilitating removal of the product from the band.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the production of sheet materials which comprises forming a sheet by the evaporative method from a solution of an organic derivative of cellulose in a volatile organic liquid, on a surface of a water soluble substance comprising a partial ester of a soap forming acid and an ether-alcohol containing at least two bydroxy groups, and stripping said sheet from said surface.

. 2. Process for the production of sheet materials which comprises forming a sheet by the evaporatlve. method from a solution of an organic derivative of cellulose in a volatile organic liquid, on a surface of diethylene glycol monostearate, and stripping said sheet from said surface.

3. Process for the production of sheet materials which comprises forming a sheet by the evaporative method from a solution of an organic derivavertical portions of the sides so that the edges .of the sheet are anchored to the horizontal portions of the "ides.

tive of cellulose in a volatile organic liquid, on a surface of glass coated with a thin layer of a water soluble substance comp'risinga partial ester of a soap forming acid and an ether-alcohol con taining at least two hydroxy groups. and stripping said sheet from said surface.

4. Process for the production of sheet materials which comprises forming a sheet by the evaporative method from a solution or an organic derivative of cellulose in a volatile organic liquid, on a surface or glass coated with a thin layer of diethylene glycol monostearate, and stripping said sheet from said surface.

5. Process for the production of sheet materials which comprises forming a sheet by the evaporative method from a solution of cellulose acetate in a volatile organic liquid, on a surface oi glass coated with a thin layer of a water soluble sub- 

